The mechanism by which HIV-associated dementia develops is unclear. It is known, however, that astrocytes, neurons, and brain capillary endothelial cells can be infected in a CD4- independent pathway, in which glycosphingolipids (GSLs) are thought to serve as receptors for HIV. Although CD4 expressing macrophages and microglial cells are the main reservoirs for HIV in the CNS, GSLs were shown to be needed for gp120 mediated fusion of CD4 expressing cells. The overall goal of the proposed research is to determine the role of GSLs in the attachment/fusion process of HIV-1 infection of CNS cells, and to inhibit that interaction. The specific aims of this proposal are to: 1) Confirm that GSLs are necessary for HIV-1 infection, and identify which GSLs are adhered to best by recombinant soluble gp120 and purified virus. This will be accomplished by determining the ability of purified GSLs, isolated from neural cells known to be infected by HIV-1, to function as ligands using TLC overlay and ELISA assays. 2) Determine which portion of the GSL(s) identified in Aim 1, interacts with gp120-the oligosaccharide, ceramide, or both. The oligosaccharide portion of the best GSL ligand will be tested for its ability to inhibit the adherence of gp120 to the immobilized GSL ligand. 3) Prepare a multivalent binding inhibitor based on the GSL moiety found to interact with gpl20 in Aim 2. Then, determine the ability of the synthesized inhibitor to block gp120 adherence to the immobilized GSL ligand, and HIV-1 entry into cultured neural cells.